1998 k2500 454 getting hot

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newguyinnc

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Do you have the correct coolant mix? And correct functioning radiator cap.
It is a big block, and will generate a lot more heat to transfer.
My 1 ton dually new had 200 or 210 thermostat. After 3000 miles I swapped it out for 185.
Going over I-80, Donner Summit, to Reno, in the bed luggage,tack, six bale's alfalfa. Pulling a two horse trailer with change storage area, never got over 200, yeah August vacation.
It sounds like you loaded a parts Cannon and blasted everything at it.
But you haven't actually found the cause.
It runs at higher temp. Does it boil over? Does it pressurize the cooling system beyond normal? Do you experience any pre-ignition.
During a loaded, working condition did the temp go unusually high, or slight equal to increased load ?
What does the service manual reference with this model and build?
What are other similar built trucks experiencing?
Have you checked for Service Bulletins on your model build or any big block trucks? That's what I would do. Good luck
Lol...I did throw a parts cannon at it, but not specifically for this particular problem. I bought this truck to tow a trailer with to make deliveries for my business. I got the truck cheap enough that I planned on rebuilding the motor anyway for piece of mind and reliability. Has correct coolant mix, not blowing anything into the overflow tank that I've been able to see. I've talked to several people with gen6 big blocks and most of them say these trucks run a little hotter on the driver's side than the passenger side of the block. The thing that has me stumped is the radiator temps are good, the temps at the thermostat housing are good and when checked with my scanner, the temp gun is within 2-3° of what the ecm says on the scanner. But the gauge sending unit in the middle of the head says 235° and I know the gauge is correct. Seems like a flow problem in the block since I've had 3 of the correct water pumps on this truck, but the motor was hot tanked by a very reputable local engine builder when he rebuilt the motor. Have a nearly identical truck to this one , same motor and tranny combination that never goes over 200° no matter what you throw at it with 185,000 miles on it.
 

454cid

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...The thing that has me stumped is the radiator temps are good...

120F sounds low to me.

, the temps at the thermostat housing are good and when checked with my scanner, the temp gun is within 2-3° of what the ecm says on the scanner.

What's the scanner saying? I don't think you've posted that, yet. Just the dash gauge, and whatever you're calling a mechanical gauge that you attached to the head.

But the gauge sending unit in the middle of the head says 235° and I know the gauge is correct.

The heads will be hotter. Are you saying that the other guage you put in the head agrees with the dash guage? What is this other gauge you're using?
 

Carlaisle

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Have you reverse flushed the cooling system? I once found a giant silicone jellyfish causing this same type of problem on a different engine. Don't assume that just because the parts are new that they are a) correct for your application or b) functional. I chased a similar overheating issue on an L29 and it turned out to be the water pump. The new/rebuilt pump had the wrong impeller installed on it. Have you tried running it with no thermostat at all? What happens if you just let it idle? What are your ambient temps?
 

newguyinnc

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120F sounds low to me.



What's the scanner saying? I don't think you've posted that, yet. Just the dash gauge, and whatever you're calling a mechanical gauge that you attached to the head.



The heads will be hotter. Are you saying that the other guage you put in the head agrees with the dash guage? What is this other gauge you're using?
The scanner says approx 200° at the intake when the gauge says 235°. The mechanical gauge I used was a brand new autometer to verify the dash gauge was correct.
 

newguyinnc

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Have you reverse flushed the cooling system? I once found a giant silicone jellyfish causing this same type of problem on a different engine. Don't assume that just because the parts are new that they are a) correct for your application or b) functional. I chased a similar overheating issue on an L29 and it turned out to be the water pump. The new/rebuilt pump had the wrong impeller installed on it. Have you tried running it with no thermostat at all? What happens if you just let it idle? What are your ambient temps?
Have not reverse flushed the system, but don't figure it needed to since this is a brand new rebuilt engine with less than 150 miles on it. I've had 2 different new water pumps on it, both reverse rotation pumps. Didn't try no thermostat at all, but did try taking the center section out of an old thermostat and using the remainder of it as a restrictor and had same results. If you just let it idle and never hit the road with it, it stays around 210°. Once you put a load to it and then idle it climbs to 235°. Ambient temps have ranged from 75° to 95° here in NC since I bought the truck and same problem no matter what the ambient temp is.
 

89GMCJOHN

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Over the years I have fixed a few hot issues and it always boils down to the same thing.... cooler thermostat , factory shroud, correct factory x numbered blade fan , HEAVY duty fan clutch p/n usually out of a 454 suburban. FWIW.
 

Schurkey

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I have a 7.4 K2500 very similar to yours, but one year older ('97). But I don't work mine hard enough to really know what temp it'll run at. However, tomorrow I'm towing a couple of cars (separately, not together) so I'll keep an eye on the temp gauge.
Only towed one car, and even that was at very low speed. So again, not much stress on the engine. Temp never went beyond 200 on the dash gauge.
 

1998crewcab

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I run a high flow water pump
Flowkooler with a high flow thermostat
With stock temp
Truck used to come to stop light and do what your truck did
But never over heated
Now it runs and needle never moves once it warmes up
Even on the hottest days it’s same temp as coldest
Glad I used the high flow water pump
 
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